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<head>
    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>
        function sum(){
            let a=prompt("输入银行卡余额")
            let b=prompt("当月食宿消费金额")
            let c=prompt("当月生活消费金额")
            console.log()
        }
    </script>
</body>
</html>